The present invention relates to the general field of lighting systems, and in particular, to large area lighting systems.
Large area lighting systems provide various levels of illumination for a variety of applications while minimizing ground level obstructions. Large area lighting systems are often used to illuminate large areas such as highways and stadiums. In densely populated areas, such large area lighting systems tend to “spill” light into nearby residential areas and thus create a nuisance for the residents. Light spillage also contributes to other problems, such as increased light pollution and sky glow. As a result, many jurisdictions have enacted laws preventing the installation of large area lighting systems in close proximity to residential areas.
There have been several unsuccessful attempts by those skilled in the art to address the light spillage issues referenced above. For example, prior art efforts have addressed light spillage problems by placing shields directly on individual lighting fixtures, see for example FIG. 1. These shields, later described in detail herein, partially restrict light from being transmitted in a particular direction, but do not efficiently or effectively eliminate the majority of unwanted light spillage. Thus, the light cut-off from such lighting fixtures is insufficient and fails to prevent light spillage from infiltrating, for example, any adjacent residential areas. Prior art shields also fail to address the issue of controlling light spillage from a combination of fixtures and thus are an inadequate solution to the problem. Moreover, prior art light shields have significant wind resistance or wind loading problems. In fact, because many prior art shields or baffles may act like a “sail” over the light pole, they create hazardous and unsafe conditions, often compromising the structural integrity of large area lighting poles and ultimately jeopardizing the safety of any potential bystanders. The effective projected area (EPA) of the structure, which generally describes the area of a given lighting unit affected by the wind, is typically and undesirably high in prior art shielded large area lighting systems. Thus, existing systems require stronger and more expensive light poles and structures to withstand the high wind loading.
Others have addressed the light spillage problem by placing shields inside the lighting fixtures. For example, some prior art luminaires are fitted with internal shields which supposedly control the emission of light only at certain specified angles. Although internal shields generally assist in directing light in a particular direction and help reduce some glare, internal shields fail to control light spillage adequately, and are not adjustable to control the amount of spillage. Internally shielded fixtures have large cut-offs and thus complicate the photometrics used in designing lighting systems. Moreover, fixtures outfitted with internal shields generally increase the expense of lighting fixtures. These fixtures often times deteriorate the light quality provided at the subject location and ultimately focus the light as a spotlight rather than an area light. Light fixtures with internal cut-off shields thus defeat the purpose of large area lighting systems.
Others in the art have fitted various types of external shields onto lighting fixtures. Although some external shields appear to provide adequate cut-off levels, they are often bulky and need to be excessively large to provide acceptable cut-off levels. Thus, prior art externally shielded lighting systems may have high EPA levels and project light similar to that found in spotlights. Thus, fitting lighting fixtures with such external shields reduces the effective and desired lighting area dramatically.
Accordingly, there is a continuing need for an effective and efficient lighting system to provide sufficient light to large areas, such as highways, while eliminating light spillage into adjacent areas, such as residential neighborhoods. What is also needed is a large area lighting system which reduces light pollution and sky glow. What is further needed is a system of maintaining area lighting capabilities at a subject site while achieving very low cut-off. What is still further needed is a system to provide effective light shielding to a plurality of light fixtures while maintaining a reduced EPA level.